Abstract: X ray diffraction (XRD) and thermogravimetric-differential scanning calorimetry (TG-DSC) were used to study the roasting decomposition and defluorination of bastnaesite. The roasting experiments of bastnaesite under air atmosphere and saturated water vapor atmosphere were carried out at the temperature from 600 ℃ to 1 000 ℃, and the roasting products were analyzed by XRD analysis and the fluoride removal rate was determined under each calcination condition. The morphology of roasting products of 600 ℃ and 1 000 ℃ were compared with a scanning electron microscope (SEM). The decomposition process and decomposition products of bastnaesite are analyzed by the experimental results. At the same time, the defluorination reaction of bastnaesite during roasting was also analyzed, and the conditions and important influencing factors of defluorination reaction were discussed. The defluorination rate of bastnaesite can reach 99.81% as it is roasted in 1 000 ℃ for 3 h under saturated steam atmosphere. A new method of enhanced defluorination of bastnaesite is proposed.